Indirect transduction methods

Indirect transduction relies on the use of indicators or labels. The first ones are based on the differences in the electrochemical behavior of indicators that interact in a different extension with dsDNA and ssDNA. The indicators for hybridization detection can be anticancer agents, organic dyes, or metal complexes, and are not generally covalently joined to DNA. The latter strategies include the use of labels covalently joined to DNA such as ferrocene, enzymes, or metal nanoparticles. 

Use of indicators Indicators are electroactive compounds that present different affinity for ssDNA and dsDNA they used to be anticarcinogenic agents, organic dyes, or metallic complexes. 

Some metallic complexes like Ru(NH3)g, [Fe(CN)6] , Co(phen)3+, or Ru(bpy)3+, and some organic compounds like methylene blue (MB) recognize the hybridization reaction. The union takes place via electrostatic interaction with the hollows of the 

Other indicators, such as daunomycin or cobalt complexes, act as intercalators. The changes in the area or peak potential of the indicator oxidation process are used as anal d ical signal [22,23]. 

Nevertheless, MB is another indicator that joins DNA by means of intercalation, but generates minor reduction signals when it is joined to dsADN than when joined to ssADN, because the specific interaction of the MB with guanine bases is lower in the dsADN. 

---

The sensitive component of an ISFET operates along the same principles as a potentiometric electrode. In both systems, there is no consumption of reaction product, and the interaction of ions with the sensitive component leads to a membrane potential. This potential is measured directly in the potentiometric electrode and indirectly in the field-effect transistor. The measurement of the activity of the ions is generally made at a constant current the measured output potential is thus a function of the ionic activity of the solution. Once the ISFET and the potentiometric electrode are covered with enzymatic membranes to give an ENFET and an enzyme electrode, respectively, the two biosensors differ only in their method of transduction. 

---